1. Field of the Invention
The present invention relates to a prober for use in making required measurements or aging tests on electric circuit elements or parts such as semiconductor integrated circuits and, more particularly, to a microprober for such a purpose.
2. Description of Related Art
Recently, there have been developed and used systems for making required characteristic measurements or aging tests on objects to be tested such as, for example, IC (Integrated Circuit) elements formed on surfaces of silicon or other semiconductor substrates, which systems are referred to as "main systems" hereinafter. Such main systems require probers for precisely and reliably making contact with pads of the objects to be tested in order to make electric connections between those pads of the objects and the main systems.
There has been an ever increasing demand for such probers that are capable of making simultaneous probing of a plurality of separate objects, or of a plurality of objects all produced on a single wafer, because defective products are detected and rejected by the characteristic measurements or aging tests on the products while they are still in wafer level and prior to dicing of wafers, thereby allowing non-defective products to proceed to subsequent steps. Such pre-selection will substantially improve the efficiency with which integrated circuits are produced, and will be particularly advantageous to the selling of integrated circuits in the form of pellets, which is commonly called "chip selling".
It is, however, very difficult to conduct high-precision and reliable probing of a plurality of objects, such as wafers, simultaneously because such objects are liable to be somewhat deformed after being subjected to different processings in the course of making integrated circuits. Hitherto, elongated metal needles have been used to get access to the objects to be tested from the circumference thereof. Some probers have a large number of elongated needles embedded in their bases with the associated springs.
Disadvantageously, such probers, using elongated needles, are large in size compared with objects to be tested and, therefore, simultaneous probing of numerous objects is impossible. Particularly, probers using spring-biased needles require high-precision machining and, therefore, it is almost impossible to make such probers perfect enough to permit simultaneous probing of a plurality of objects to be tested. Such probers are not suitable for mass production and, if actually made, would be very expensive.
An accelerated aging is effected in heating and cooling cycles ranging from the room temperature to 125.degree. C. If the thermal expansion coefficients of probers are different from those of objects to be tested, prior art probers cannot assure good contact with such objects. As a tendency, wafers have been increasing in size to, say, eight inches and, accordingly, such large-sized wafers are liable to cause increased thermal expansion. It has, therefore, been difficult for such prior art probers to make the simultaneous probing of a large number of objects or elements and/or parts on such a large-sized wafer.
The difficulty with which simultaneous probing is effected will increase with an increase in the number of objects because of the difficulty in assuring good contacts between probers' contacts and objects' pads due to the warp or unevenness of wafers. In order to overcome such a circumstance, a prober has been designed with such a size that it includes only one or a few contact blocks having contacts corresponding the pads of one object to be tested. Such a prober is operated to sequentially move across the objects for making measurement thereof. As a matter of course, a burn-in operation which requires the simultaneous probing of all objects is impossible.
The probers handling a plurality of objects are often designed so as to permit different signals such as chip select, chip enable and output enable signals to be directed to the selected objects via a common bus including data and address lines, thus permitting sequential access to individual objects.
Consequently, presence of any defective element among those under simultaneous probing for measurements or tests may cause an adverse effect on the level of address or data information from other elements accessed, and therefore, wrong information may result.